Regarding the gray scale driving method of a display element such as an optical modulation element, many types of display devices have conventionally adopted a device arrangement or a multi-level gray scale driving method for carrying out multi-level gray scale display.
For instance, Japanese Laid-Open Patent Application No. 2000-347624 (Tokukai 2000-347624; published on Dec. 15, 2000), Japanese Laid-Open Patent Application No. 2000-284751 (Tokukai 2000-284751; published on Oct. 13, 2000), and Japanese Laid-Open Patent Application No. 8-129359/1996 (Tokukaihei 8-129359; published on May 21, 1996) disclose gray scale display means of a display element of a conventional electroluminescence display device.
The gray scale display means defined in the publications above is arranged such that TFTs for driving a display element are connected in parallel with each other, and the multi-level gray scale display is carried out by controlling the electric conductivity of each TFT.
Also, Japanese Laid-Open Patent Application No. 2000-310980 (Tokukai 2000-310980; published on Nov. 7, 2000) discloses a method of realizing the maximum-level gray scale by converting the input gate voltage of a drive TFT to multi-level and carrying out a time division gray scale driving.
In this arrangement adopting the time division gray scale driving method, the optical modulation element itself carries out precise analog gray scale driving.
However, the conventional multi-level gray scale driving methods carrying out the analog gray scale driving have a problem such that the fluctuation of the output current due to the fluctuation of the gate input voltage of the drive TFT causes the occurrence of significant luminous transition in the display, since the element emits light by the current control.
Thus, to solve this problem of the luminance transition, the multi-level gray scale display has recently been realized by adopting binary drive which has few problems with the stability of output luminance control, and time-dividing the binary display.
However, if the conventional multi-level gray scale driving method in which the binary display is time-divided is adopted, a display device such as a plasma display device, which is intrinsically able to carry out only the binary display, controls sub fields corresponding to the bit weight of each gray scale signal information by adopting the time division method. On this account, a dynamic false contour is generated and hence the multi-level gray scale display cannot be properly carried out.
This dynamic false contour becomes visible owing to the synergistic effect of (i) the amount of travel of the luminous barycenter within the field period being maximized in the field period of the greatest weight and (ii) the luminous barycenter and the sight line of the viewer moving in accordance with the movement of images, and hence the image quality is degraded.
To solve this degradation of the image quality due to the occurrence of the dynamic false contour, for instance, Japanese Laid-Open Patent Application No. 9-83911/1997 (Tokukaihei 9-83911; published on Mar. 28, 1997) and Japanese Laid-Open Patent Application No. 10-124001/1998 (Tokukaihei 10-124001; published on May 15, 1998) disclose a display device which carries out the time division gray scale driving of the binary display, such as a plasma display device, etc.
In the display device defined in the publications above, a display element can independently carry out gray scale display of 2-4 bits precisely. However, to realize the maximum-level gray scale display, it is necessary to restrain the occurrence of the dynamic false contour under the limit, while carrying out the time division display. Thus, this display device has time division periods provided in a plurality of sub fields which exceed the number of display bits, so that the occurrence of the dynamic false contour is restrained.
However, since the display devices of the publications above require the transfer of a gray scale signal of each bit to the pixels in each scanning, the number of driving of the driver for gray scale drive provided in the display device increases, and this puts a load on the driver for gray scale drive.
Moreover, in accordance with the increase of the number of driving of the driver for gray scale drive, the power consumption of the display device also increases.